Polyarylene sulfides are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide variety of applications. Polyarylene sulfides are generally formed via polymerization of a dihaloaromatic compound with an alkali metal sulfide or an alkali metal hydrosulfide in an organic amide solvent. Salts are formed as byproducts in the polymerization reaction, and these salt byproducts must be removed to obtain a final product exhibiting desirable traits.
Standard methods for removal of salt byproducts have included the utilization of screens or sieves that rely on a difference in particle size between the polyarylene sulfide and the salt byproduct. Unfortunately, these methods have proven less than ideal due to loss of product in the form of polyarylene sulfide fines as well as undesirable levels of salt byproduct remaining trapped in the product polyarylene sulfide granules. Water extraction has been utilized in an attempt to remove salt remaining after the screening/sieving operation, but this adds an additional step as well as associated costs to the to the formation process and does not solve the problem of the loss of polyarylene sulfide fines during the screening/sieving operation.
Solid/liquid extraction processes have also been utilized to remove salt byproducts from the polymerization product. While fairly effective, extraction methods require a large amount of water and thus create both waste and additional operational costs. Other separation processes such as flashing of solvent followed by sieving and/or water extraction have been utilized, but these methods, similar to others, add costs, additional process steps, and undesirable waste to the formation process.
What is needed in the art is a method for removal of salt byproducts during formation of a polyarylene sulfide polymer that can keep capital costs low and avoid the formation of additional waste.